[CIG-SHORT] nondimensionalization question

[Lucas Abraham Willemsen]

Hi,

In preparation for my research I am currently investigating the nondimensionalization implementation in Pylith. The way I understand things is that nondimensionalization should have no effect as long as the double precision is good enough in preventing round-off errors. I used a dynamic simulation with a slip-weakening fault in order to test this theory. When I use a dynamic nondimensionalization object everything is as expected. Changing the scales 'shear_wave_speed', 'mass_density' and 'wave_period' has no effect on the final displacement.

I was told (maybe in error?) that both dynamic and quasistatic nondimensionazation objects are valid in a dynamic simulation and should give the same result (they do the same thing?).  But when I test this it does not work. changing any of the scales in the quasistatic nondimensionalization object changes the final displacements significantly (orders of magnitude).

I browsed around in the source code for the implementations of the objects and I found this. It does seem like both these objects essentially do the same thing (except for the fact that the quasistatic object will always have a default density scale since it is intended for quasistatic problems).

http://geodynamics.org/svn/cig/cs/spatialdata/tags/v0.5.2/spatialdata/units/NondimElasticDynamic.py
http://geodynamics.org/svn/cig/cs/spatialdata/tags/v0.5.2/spatialdata/units/NondimElasticQuasistatic.py

(it says v0.5.2 in the link, but there is no higher one. Is this what is currently used? Could not find the files in the source code download)

A test project can be found here: http://web.mit.edu/lawillem/www/nondimtest.zip

Note how changing the dynamic scales changes nothing, while the quasistatic ones do influence the final displacements significantly.

best,
Lucas

P.S. My motivation for this question is that I plan to investigate the difference between a quasi-static and dynamic simulation with rate and state friction. In order to make the transition from dynamic to real quasistatic (implicit formulation) I first wanted to change the nondimensionalization object to quasistatic (while problem remains dynamic, explicit timestep) and get the same results.
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